The usual classification
according to the general design of the milling machines is as follows: -
(a) Column and knee type milling
machine
(i) Horizontal
milling machine (Plain)
(ii) Universal
milling machine
(iii) Omniversal
milling machine
(iv) Vertical
milling machine
(b) Bed or manufacturing type
milling machine
(i) Simplex
milling machine
(ii) Duplex
milling machine
(iii) Triplex
milling machine
(c) Special type
(i) Rotary table
milling machine
(ii) Drum
milling machine
Column and Knee Type Milling Machine
For general workshop the most
commonly used is the column and knee type. These machines have a single spindle
only. They derive their name “Column and Knee” type from the fact that the work
table is supported on a knee like casting which can slide in a vertical
direction along a vertical column. The up and down movement of the table can
accommodate work of various heights.
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| Column and Knee Type Milling Machine |
Main Parts
Main parts of column and knee
milling machine are as follows.
(a) Base - The base of machine is a grey cast iron casting provided at
the bottom of the machines. It is accurately matching on both top and bottom of
the machine surface. Column of the machine is secured to its base and serves as
a reservoir for the coolant.
(b) Column - It is a very prominent part of milling machine. The column
is box shaped heavily ribbed in side and houses all the driving mechanism for
the spindle and table feed. The front vertical face of the column is accurately
machined and is provided with dovetail guide ways for supporting the knees. Top
of the column carries dovetail in horizontal ways for the over arm.
(c) Knee - It is the rigid casting which is capable of sliding up and
down along the vertical ways on the front face of the column. The adjustment of
the height is affected by elevating screw mounted on the base that also
supports the knee. The knee houses the feed mechanism of the table and
different controls to operate it. The machine horizontal ways are provided on
the top surface of the knee for the cross traverse of the saddle and hence the
table. For efficient operation of the machine, rigidity of the knee and
accuracy of its ways play an important role. On the front face of the knee two
bolts are usually provided for securing the braces to it ensure greater
rigidity under heavy loads.
Plain Milling Machine
These machines are of the column
and knee type and consist of a rigid frame or box structure. It consists of a
table, a saddle and a knee. This gives three straight-line movements
perpendicular to each other. The arbor is fixed in position, and the tool
rotates while the work is fed past the cutter in a straight line. It is a
useful machine for manufacturing operation involving simple, straight line cut.
Universal Milling Machine
A universal milling machine is so
named because it may be adapted to a very wide range of milling operation. A
universal milling machine can be distinguished from a plain milling machine
that the table of a universal milling is mounted on a circular swivelling base
which has degree graduations and the table can be swivelled to any angle up to 450
on either side of the normal position. This is advantageous when milling
spirals. Thus in a universal milling machine in addition to three movement as
incorporated in a plain milling machine, the table may have a fourth movement
when it is fed at an angle to the milling cutter.
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| Universal Milling Machine |
Omniversal Milling
Machine
In this machine, the
table having all the movements of a universal milling machine, and can be
tilted in a vertical plane by providing a swing arrangement at the knee. The
entire knee assembly is mounted in such a way that it may be fed in
longitudinal direction horizontally. The additional swivelling arrangement of
the table enables it to machine taper spiral grooved in reamers, bevel gears
etc it is essentially a tool room and experimental shop machine.
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| Omniversal Milling Machine |
Vertical Milling Machine
There are two types of vertical
spindle milling machines.
(a) Fixed bed type (b) Column and knee type. A vertical milling machine can be
distinguished from a horizontal milling machine by the position of its spindle,
which is vertical or perpendicular to the work table. The machine may be a
plain or universal type and has all the movements of the table for proper
setting and feeding the work. The spindle head which is clamped to the vertical
column may be swivelled at an angle, permitting the milling cutter mounted on
the spindle to work on angular surfaces. In some machine the spindle can be
adjusted up or down relative to the work.
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| Vertical Milling Machine |
Bed or Manufacturing Type Milling Machine
(a) Horizontal Simplex Milling Machine - These types of machines are
production type machines and are of rigid structure which yields high
production of interchangeable jobs. It has got one spindle head.
(b) Horizontal Duplex Milling Machine - Milling machines using the two
spindles. for finishing two surfaces of casting at a time.
(c) Triplex Milling Machine - Milling machines using the three spindles, two horizontal
and one vertical for finishing three surfaces of casting at a time.
Planner type Milling
Machine
They are used for heavy work.
Upto a maximum of four tool heads can be mounted over it, which can be adjusted
vertically and traverse directions. It has a robust and constructions like a
planer.
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Special type Milling Machine
(a) Continuous Feed Rotary Milling Machine - The construction of the
machine is a modification of a vertical milling machine and adapted for
machining flat surfaces at production rate. The face milling cutters are
mounted on two or more vertical spindles and a number of work pieces are
clamped on the horizontal surface of a circular table which rotates about
vertical axis. The cutters may be set at different heights relative to the work
so that when one of the cutters is roughing the pieces the other is finishing
them. Operator may carry out a continuous loading and unloading of the work
pieces, while the milling is in progress.
(b) Drum Type Milling Machine - The drum type milling machine is
similar to rotary table milling machine in that its work supporting table which
is called a drum, rotates in a horizontal axis. The cutters are face mills and
are usually roughing and finishing cutters similar to those of a rotary table
miller. Fixture is mounted to the drum either on each face or on the periphery.
When the work is mounted on the periphery, the operation is usually facing the
two ends of the work piece to the precise length. The finished machined parts
are removed after one complete turn of the drum and then new ones are mounted on
it.
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Drum Type
Machine
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